Insect Transgenesis: Mechanisms, Applications, and Ecological Safety

Abstract

The ability to routinely genetically modify insect species holds great promise for fundamental research that explores the functional activity of genomic sequences, and the use of this information to control the viability, fitness, and behaviour of both beneficial and pest insects. Currently, almost all insect genetic modifications rely on the use of transposon vector systems, and a detailed understanding of the mechanisms that result in mobility is critical to applications that require optimal or maximum frequencies of transposition, and to applications where immobilization is necessary for vector stabilization. Great progress has been made in understanding the biophysical mechanisms and interactions between the transposase enzyme for the Hermes and Mos1 transposons and their respective ITR sequence substrates, but the relevance of this knowledge to other transposon vectors can only be speculated upon. It is clear, however, that mutations in the transposon sequence can result in their hyperactivity, and an effective means of screening for these mutations should improve our understanding and applied use of all the available vectors. Progress also has been made in testing recombinant-based constructs for their ability to diminish the vectorial capacity of mosquito disease vectors, but the ability to drive these transgenes into an endemic population is largely unknown. Genetic drive systems, such as autonomous vectors or meiotic drive, have been speculated upon, but serious testing in targeted species remains to be done. Development of transgenic strains for biocontrol has also been initiated, especially for tephritid fruit flies, and conditional lethality systems may supersede current programmes such as SIT. To do so, nearly complete, if not complete lethality will be needed at a consistent level, and model systems have yet to achieve this. To develop such strains, repetitive introductions of transgene vectors into a host genome may be required, but a difficulty in comparing efficacy is the varying influence of different insertion sites on transgene expression and host fitness. A prospective problem for transposon-mediated vector insertions is the potential re-mobilization of the vector by an unintended source of transposase. The development of a new class of vectors that allow genomic targeting by RMCE, and transposon immobilization by ITR deletion, should have a significant impact on the efficient creation and testing of new transgenic strains, as well as minimizing the ecological risk of their release into the environment.